Oil premix burner

ABSTRACT

An oil premix burner comprising: a combustion element; a burner surface on the outer lateral surface; a distribution chamber below the burner surface; a central oil injection device; a combustion air channel connected to a blower situated upstream as well as an air heat exchanger for the preheating of the combustion air in the area of the burner surface. In each case, the annular space formed between the inner tube and the outer tube of all the double tube elements opens out into an annular-shaped collecting chamber, and the preheated combustion air, starting from the collecting chamber, flows inwards via a swirl-generating device into the area around the oil injection device into the distribution chamber.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an oil premix burner having a combustion element.

2. Description of the Related Art

Such oil premix burners have a cylindrical combustion element having a burner surface on the outer lateral surface. Round about a central oil injection device there is a distribution chamber, as a rule, for the oil mist being created, so that the latter uniformly reaches the burner surface from within. The combustion air gets into the distribution chamber via at least one inflow opening in the vicinity of the oil injection device, which may be an injection valve or an oil nozzle which is fastened to a nozzle holder having an oil preheater. Upstream of the oil injection device there is a combustion air channel having a connection to a blower.

In the case of gas burners, in particular, which are operated in a modulating manner, that is, in which the performance range is able to be controlled between a small proportion of the maximum performance and the maximum performance, the so-called premix burners have proven successful. In these burners, the fuel and the combustion air required for its combustion are mixed locally separated from the flame and are then combusted. For this purpose, a cylindrical combustion element is mostly used as flame holder, which is permeable to the fuel/air mixture and encloses an internal space to which the fuel/air mixture is supplied. Using this technology, small flames are able to be realized having good exhaust gas values, relatively small flame holders and large modulation ranges.

The basic principle of an oil premix burner is the mixing of finely atomized oil with preheated air. Because of this principle, it is possible that a so-called cold flame forms, for example, so that the fuel is able to be combusted over a surface. The surface combustion is, however, also possible without a cold flame. Generally, the heating of air is relatively difficult because of its low heat capacity, because to do it, either an effective heat transition via a wall to the air flow and/or high wall temperatures are required.

An oil premix burner is known, for instance, from published German patent application document DE 10 2006 000 174 A1. In this case, the fact is used that hot air vaporizes the oil, and consequently a gas mixture is able to be formed which, just as in a gas premix burner, moves all the way through the flame holder and burns off. By the admixture of exhaust gas to the combustion air for preheating the air, the formation of nitrogen oxides is reduced in addition, and it is intended that thereby the start-up response is improved, because the operating point is reached relatively rapidly. The combustion air is guided for the take-up of heat by a conducting device that rises, at least in sections, over a burner surface and is guided at a distance from the burner flame, and is accelerated in a nozzle in the guiding device, so that the exhaust gas is able to be aspirated from the combustion chamber and mixed with the air.

Published German patent application document DE 26 43 293 Al also describes such a channel for the combustion air, which is situated as a cylinder about the rear region of a fuel rod or combustion element. Since, for the mixing and the combustion reaction, a certain minimum combustion element diameter is required, this design may lead, however, to an overall relatively large combustion chamber compared to known designs.

Furthermore, from published German patent application document DE 21 07 514, a device is known for heating using infrared radiation, and from U.S. Pat. No. 1,082,576, an oil burner is known having planar, closed, continuous channels for air preheating that are situated in a planar manner below the burner surface. From these uninterrupted channels, the preheated air is in both cases conducted back to the center with the fuel supply and is mixed there with fuel. Starting from this center, the mixture enters the combustion zone, without coming again into the vicinity of the air flow path used for the preheating.

An oil premix burner is known from German utility model DE 20 2008 005 913 U1, in which an air heat exchanger is assigned for the preheating of the combustion air, which is made up of at least one channel encompassing the combustion element at a distance. It is made up of channels running next to one another, situated in parallel, but flowed through in series, which are both acted upon from the outside by heat from the burner flame.

Published German patent application document DE 10 2010 046 733 A1 relates to an air heat exchanger made of at least one double tube element having an inner tube flowed through in series and an outer tube concentric to it. In this context, the air heat exchanger is situated above the burner surface and is made up of a plurality of double tube elements that are distributed symmetrically over the circumference and extend having parallel axes to the combustion element at least over a part of its length and are flowed through in parallel. In this instance, each double tube element has a turnaround zone at the end face of the free end as a connection between the inner tube and an annular space formed between the inner tube and the outer tube.

Consequently, each double tube element is connected to the combustion air channel at its entry side of the inner tube. There the combustion air enters and in each case, after leaving the inner tube at a turnaround zone, it gets to the end face of the free end into the annular space formed between the inner tube and the outer tube. In this annular space, there flows the air, already preheated, back in the direction of the end face close to the oil injection device, and absorbs additional heat. There, it enters into the distribution chamber as preheated combustion air in the region about the oil injection device. In one preferred specific embodiment, in a double tube element, the inner tube projects beyond the outer tube in the longitudinal direction at the end near the oil injection device, so that it reaches through the discharge region of the annular gap that is in connection with the distribution chamber and reaches through a limiting wall all the way into the combustion air channel.

BRIEF SUMMARY OF THE INVENTION

The present invention is therefore based on the object of optimizing the combustion quality and the robustness, particularly with respect to the modulation capability, of an oil premix burner.

The oil premix burner is characterized in that, in each case, the annular space formed between the inner tube and the outer tube of all double tube elements opens out into an annular-shaped collection chamber, and the preheated combustion air, starting from this collection chamber, flows inwards via a swirl-generating device into the area around the oil injection device into the distribution chamber. For this purpose, the swirl-generating device, having flow from the outside to the inside, is developed ring-shaped and symmetrically to the center of the oil injection device.

In one preferred specific embodiment, the swirl-generating device is designed as an annular disk, which is enclosed on both sides in the axial direction by associated limiting walls and has channels in the radial direction for the combustion air. In this context, the swirl-generating device is preferably developed as an annular disk and, in the circumferential direction, has a uniform wave-shaped construction of alternating channels, the wave-shaped outer sides each lying against associated limiting walls, and between the internal wave sides and the limiting walls, lying respectively opposite, a channel is developed in each case for the combustion air.

For the combustion air, the channels advantageously have the form of flat channels in each case having an essentially rectangular flow-through cross section. The outer wave sides are each equipped with one elongated hole which runs in the direction of a channel, and is used among other things, for welding onto a limiting wall, as well as for tension equalization during a bending process.

In one preferred specific embodiment, the channels of the swirl-generating device have a radial angle of incidence, this amounting to approximately within the range of 30 degrees to 75 degrees to the mid-perpendicular.

A further advantageous specific embodiment provides that the swirling direction able to be achieved using the swirl-generating device is adjusted to the central oil injection device, especially its spraying behavior. In this context, preferably the swirling direction of the air flow accelerated using the swirl-generating device is equal to the swirling direction of the oil spray accelerated correspondingly using the central oil injection device. This combination effects relatively long eddies having a corresponding effect on the flow until far into the distribution chamber. Thus there comes about an intensive and as homogeneous as possible a mixing through of oil mists with the combustion air.

In one preferred specific embodiment, an associated cone is situated at a distance about the central oil injection device, which forms the transition of the limiting wall close to the combustion rod of the swirl-generating device into the distribution chamber. The cone preferably extends at least over about one-fifth of the length of the distribution chamber and tapers in the flow direction in such a way that the entry diameter is at least 5 percent greater than the exit diameter.

The outer diameter of the swirl-generating device is advantageously less than the pitch diameter of the double tube elements and the internal diameters of the swirl-generating device are designed to be greater than, or equal to the inner diameter of the cone about the central oil injection device.

Using the measures according to the present invention, both the combustion quality and the robustness are improved in oil premix burners. The system according to the present invention having the integrated air heat exchanger is advantageous, particularly for modulating operation. This applies for burners having a cylindrical combustion element the same as for batwing burners having a horizontal burner surface and the design according to the invention. The flame burns on, or rather in the burner surface, so that, in the process, above it, energy is coupled out and used for heating the combustion air. That being the case, one may omit electrical air preheating during the stationary burner operating state. This has a positive effect on the energy balance of the burner.

One considerable advantage of the air preheating function according to the present invention is that with increasing burner surface, for instance, in a combustion element for larger performance ranges, the heat exchanger surface may also be extended to the same degree, by simply using longer double tube elements. With that, the air temperature striven for remains constant. Each tube is defined by its specific performance density and the number of tubes as a function of the overall performance. Besides on the double tube elements of the air heat exchanger, thereby no constructive changes are required, for the representation of different burner performance variables, on the periphery or other burner components. Thus, the remaining burner construction is maintained exactly as the requirements on the surrounding combustion chamber. An enlargement of the passage cross section in the swirl-generating device developed as an annular disk is very simply implemented by increasing the wave-shaped forming. Then, one only has to offset the limiting wall directed upstream, i.e. towards the combustion air channel, slightly, in order to equalize the gap width for a slightly thicker annular disk.

Using the air heat exchanger according to the present invention, combustion air is to be provided at all burner operating points having a minimum temperature of ca. 350° C. In this context, one should note that the maximum admissible surface temperature at the air heat exchanger is maintained. In addition, an intensive swirling of the entire preheated air flow is achieved in the immediate vicinity of the oil injection device. Varying the swirl-generating device, particularly the annular disk is easily possible. Therefore, from performance variable to performance variable, an adjustment of the swirling effect may take place, for example. This is meaningful in the case of different and especially adapted oil injection devices, for instance, having a changed spray image, a varying spray intensity or a specified rotation of the spray image. Consequently, an intensive and complete thorough mixing is assured of oil mists and combustion air for various performance variables and different operating states.

The present invention also yields advantages with respect to very slight pressure loss and scalability in the supply path of the combustion air.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an oil premix burner in longitudinal section.

FIG. 2 shows a perspective view of a swirl-generating device.

DETAILED DESCRIPTION OF THE INVENTION

The oil premix burner is made up essentially of a combustion element 1, having a burner surface (not shown) on the outer lateral surface, a distribution chamber 2 below the burner surface, a central oil injection device 3, a combustion air channel 4 connected to a blower situated upstream as well as an air heat exchanger for the preheating of the combustion air in the area of the burner surface. The latter is made up of a plurality of double tube elements 5 that are distributed over the circumference, that extend with their axes parallel to combustion element 1 and have parallel flows through them, and having an inner tube 6 and an outer tube 7 having flows through them in series. In this context, each double tube element 5 is connected with the entry side of inner tube 6 to combustion air channel 4. The combustion air, in each case, in a turnaround zone 8 at the end face of the free end gets into annular space 9 that is formed between inner tube 6 and outer tube 7, and flows back in the direction of the end face close to the oil injection device.

At that location, annular space 9 of all double tube elements 5, formed in each case between inner tube 6 and outer tube 7, opens out into an annular collecting chamber 10. After that, the preheated combustion air, starting from this collection chamber 10, flows inwards via a swirl-generating device 11, into the region about oil injection device 3, into distribution chamber 2.

For this purpose, swirl-generating device 11 is developed to be annular and symmetrical to the center of oil injection device 3. Preferably this is as an annular disk, which is enclosed on both sides in the axial direction by associated limiting walls 12, 13 and has channels in the radial direction for the combustion air. In the circumferential direction there comes about a uniform wave-shaped construction of alternating channels, the wavy outer sides 14, 15 lying in each case against limiting walls 12, 13 and between the waves' inner sides and the respectively opposite limiting wall 14, 15 a flat channel is developed in each case for the combustion air. The outer wave sides 14, 15 are each equipped with one elongated hole 16, which runs in the direction of a channel, and is used among other things, for welding onto a limiting wall 12, 13 as well as for tension compensation during a bending process.

At a distance round about central oil injection device 3 there is situated an associated cone 17, which forms the transition of limiting wall 12, close to the fuel rod, of swirl-generating device 11 into distribution chamber 2. Cone 17 extends at least over about one-fifth of the length of distribution chamber 2 and into it, and tapers while on this path. 

What is claimed is:
 1. An oil premix burner, comprising: a combustion element; a burner surface on an outer lateral surface; a distribution chamber below the burner surface; a central oil injection device; a combustion air channel connected to a blower situated upstream; and an air heat exchanger for preheating combustion air in an area of the burner surface, the air heat exchanger including multiple double-tube elements distributed over the circumference; wherein the double-tube elements have parallel flow-through and extend to the combustion element along parallel axes, and wherein each double-tube element has an inner tube and an outer tube having flow-through in series with one another, each double tube element having an entry side of the inner tube connected to the combustion air channel; wherein the combustion air, in a turnaround zone at an end of each double-tube element away from the oil injection device, enters an annular space formed between the inner tube and the outer tube, and subsequently flows back in the direction of the entry side near the oil injection device; wherein the annular space formed between the inner tube and the outer tube of each double-tube element opens out into an annular-shaped collecting chamber; and wherein the preheated combustion air, starting from the collecting chamber, flows inwards via a swirl-generating device into an area around the oil injection device into the distribution chamber.
 2. The oil premix burner as recited in claim 1, wherein the swirl-generating device is configured to conduct the flow of the preheated combustion air from the outside of the swirl-generating device to the inside, and wherein the swirl-generating device is ring-shaped and symmetrically to the center of the oil injection device.
 3. The oil premix burner as recited in claim 2, wherein the swirl-generating device is configured as an annular disk which (i) is enclosed on both sides in the axial direction by associated limiting walls and (ii) has channels in the radial direction for the combustion air.
 4. The oil premix burner as recited in claim 2, wherein the swirl-generating device is configured as an annular disk and, in the circumferential direction, has a uniform wave-shaped construction of alternating channels, wherein wave-shaped outer sides each lie against associated limiting walls, and between wave-shaped internal sides and the limiting walls, lying respectively opposite one another, a channel is provided in each case for the combustion air.
 5. The oil premix burner as recited in claim 4, wherein each channel for the combustion air is configured as a flat channel having an essentially rectangular flow-through cross section.
 6. The oil premix burner as recited in claim 3, wherein the channels of the swirl-generating device have a radial angle of incidence to the mid-perpendicular within the range of approximately 30 degrees to 75 degrees.
 7. The oil premix burner as recited in claim 4, wherein a swirling direction achieved by the swirl-generating device is adjusted based on oil spraying characteristics of the central oil injection device.
 8. The oil premix burner as recited in claim 7, wherein the swirling direction of the air flow accelerated using the swirl-generating device substantially corresponds to the swirling direction of the oil spray generated using the central oil injection device.
 9. The oil premix burner as recited in claim 4, wherein a cone is provided at a distance from the central oil injection device and concentric with the central oil injection device, the cone forming a transition of one of the limiting walls of the swirl-generating device into the distribution chamber.
 10. The oil premix burner as recited in claim 9, wherein the cone extends over at least approximately one-fifth of the length of the distribution chamber and tapers in the flow direction in such a way that an inner entry diameter of the cone near the central oil injection device is at least 5 per cent greater than an inner exit diameter of the cone away from the central oil injection device.
 11. The oil premix burner as recited in claim 9, wherein an outer diameter of the swirl-generating device is less than a pitch diameter of the double-tube elements, and wherein an inner diameter of the swirl-generating device is at least equal to the inner entry diameter of the cone about the central oil injection device. 